In mobile communication networks like GSM, UMTS or Long Term Evolution (LTE) networks, as illustrated on FIG. 1, a primary station 100 communicates with a plurality of secondary stations 110. These secondary stations 110 are typically handheld devices including batteries 111 supplying a communication device 112. To extend the operation time of the secondary stations without increasing the size of the batteries, it is currently desirable to reduce the power consumption of the secondary stations (or User Equipments (UEs)). In addition, if the battery charge becomes depleted, rather than exhaust the remaining energy, it would often be desirable to further reduce power and conserve energy, for example by adopting a more limited form of operation with reduced performance or fewer supported services.
It could be possible for example to transmit to the primary station a power limitation indicators, whose purpose is to allow the secondary station to indicate to the primary station and fixed network a condition of limited power availability. These indicators may be used to differentiate between devices that are mains-powered like secondary station 110b and those that are battery-powered or to indicate a low battery status.
When a secondary station registers for the first time (and on infrequent occasions thereafter), it indicates to the fixed network its capabilities via the UE Capabilities information elements or a UE category. This information could include, for example the number of UE Rx antennas and the maximum data rate that the UE can receive. The fixed network therefore has knowledge of what the UE is physically capable of doing and can instruct the UE to behave in accordance with network requirements and capacity, data delivery requirements and the UE's own operational limits.
It is to be noticed that it is difficult to define the threshold for signalling a change in status in a way that allows the primary station or fixed network to consistently respond in a meaningful way. Should it be sent at 50% battery capacity? 20%? 10%? Given that battery capacities vary according to the secondary station, like the battery size, technology and ageing and given that secondary station power consumption depends somewhat on implementation details, it would not be clear what, for example, “50% battery capacity” would actually mean for the secondary station. It is also not clear what it would mean for a user. Does he expect to be able to place the secondary station on charge or does he prefer to economise on energy consumption as much as possible?
As well as a shortage of battery power, the available signal processing power or signal reception capability of the terminal may also depend on whether other events occurred or features (such as reception of MBMS (Multicast/Broadcast Multimedia Services) or other transmissions or processing the output of a video camera) are currently in use or not.